Single pin oscillators are desirable in integrated circuit (IC) configurations. A basic oscillator is contained within the IC but the frequency determining components are external to the IC to avoid committing the device to a restricted frequency range. Also, since the external components can be manufactured or selected to any desired tolerance, the frequency tolerance is not confined to the IC. Since the frequency determining element is external, at least one pin must be added to the IC housing. Desirably only one pin is added to those already needed to operate the IC. This is usually accomplished by employing one or more of the other pins for plural function.
Previous attempts have been made to connect an RC combination to an IC to provide the oscillator function. Basically the resistor and capacitor are series connected between the power supply terminals. The juncture of the resistor and capacitor is connected to a separate IC input pin. The IC periodically discharges the capacitor after it has been charged to a particular threshold. Thus the circuit oscillates between ground potential and some IC-established threshold potential. One difficulty with this approach is that the IC produced threshold is a function of the power supply potential. Thus, oscillator frequency is related to potential unless some form of compensation is employed. Such compensation is difficult and often is effective over only a limited range of potentials.
Another difficulty is associated with IC manufacture. Process variables are always experienced to some degree. Since the threshold potential is internally set, it will be subject to variation from one IC to the next and from one batch of IC's to the next batch.